1. Field of the Invention
The present invention relates to a microwave detector, and in particular relates to a wideband microwave detector capable of detecting microwaves in a plurality of different bands.
2. Description of the Prior Art
In general, prior art microwave detectors are equipped with a reception system in which microwaves are picked up or detected by an antenna and mixed with the output of a local oscillator which carries out a sweep over a prescribed sweep frequency to create an intermediate frequency signal that then undergoes amplification and wave detection.
Further, in the case where the detection target microwaves are present in a plurality of bands, the microwave detector needs to be able to carry out multi-band and wide-band operations. In such case, the number of reception systems connected to the antenna in the prior art microwave detector is increased to match the number of microwave frequency bands requiring detection. In other words, a reception system is established for each detection target band, and each of such plurality of reception systems is constructed from a local oscillator that oscillates at a prescribed frequency in accordance with a corresponding detection target band, and an intermediate frequency amplifier established in a pass frequency band in accordance with the corresponding detection target band.
Further, such plurality of reception systems is connected to the antenna in a parallel arrangement, and a selection means (e.g., a selector switch) is provided to alternatively select any one of the reception systems. With this structure, by using the selection means to select one reception system at a time in a sequential manner, it becomes possible to detect microwave signals present in a plurality of detection target bands.
However, the prior art microwave detector which is capable of multi-band and wide-band operations described above has the following problem. Namely, because each detection target band is sequentially selected one at a time to undergo a detection process, a relatively large amount of time is required to search all the detection target bands. In particular, this problem gets worse as the number of detection target bands is increased.
Further, in the case where the microwave detector is mounted in a motor vehicle (e.g., a car or a motorcycle) to detect microwave signals emitted from a radar type speed measurement device, because the vehicle will travel a relatively long distance during the time it takes to search all the detection target bands, there is the risk that the vehicle will reach a position near the radar type speed measurement device before detection of such microwave signals.
Furthermore, in the case where the microwave detector operates intermittently to conserve electricity, because an even greater amount of time will be required to search all the detection target bands, the problem described above (i.e., a long response time) is made worse. Further, if the suspension time is reduced in an attempt to alleviate such problem, the power conserving effect of such a microwave detector will be degraded.